A. Field of the Invention
The invention relates to a hydraulic cement slurry, to a dimensionally stable solid formed when the slurry sets, and to a method for cementing wells using the slurry. A key feature of all aspects of the invention is a particular set retarder component in the slurry.
B. Description of the Prior Art
Hydraulic cements, i.e., any inorganic cement that hardens or sets under water, are customarily admixed with water and emplaced as aqueous slurries. The amount of water employed may vary rather extensively dependent largely upon the fluidity of the slurry required and upon the necessary ultimate strength. Various functional additives may be employed to modify the properties of the basic cement slurry.
In cementing operations, particularly in moderate and high temperature environments such as may be encountered in well cementing, for example, it is often necessary, or at least highly desirable, to retard the rate at which a cement slurry would normally set in order to provide an adequate thickening time to permit placement of the cement slurry where desired. Martin, U.S. Pat. No. 3,100,526, teaches glucoheptonic acid or a water-soluble salt thereof, preferably sodium glucoheptonate, as a retarder. Walker, U.S. Pat. No. 3,053,673, teaches a two component retarder system comprising a lignin derivative, i.e., a lignosulfonic acid salt, and either gluconic acid, gluconic acid delta lactone, or an alkali metal, ammonium, or alkaline earth metal gluconate.
Another class of functional additives for cement slurries is a fluid loss control additive. In a great many uses of a hydraulic cement it is necessary for the cement slurry to be emplaced within or next to a porous medium, for example, earthen strata, e.g., in the cementing off of boreholes, grouting, dam and tunnel construction and the like. When such is the case, water filters out of the slurry and into the strata during the setting period. When this occurs to any appreciable extent there usually results an uncontrolled setting rate, improper placement, impaired strength properties and usually a contamination of the surrounding strata. All of these undesirable conditions are especially to be avoided in cementing operations associated with oil, gas, water or brine wells. In an effort to lessen the loss of fluid from an aqueous hydraulic cement slurry various materials have been employed. One such material comprises a polyamine compound selected from the class consisting of polyalkyleneimines, polyalkylenepolyamines and mixtures thereof. A description of these polyamine compounds and their use in hydraulic cement slurries is taught, for example, by Gibson et al., U.S. Pat. No. 3,491,049, the teachings of which are specifically incorporated herein by reference.
It is often desirable to include additives both to reduce fluid loss from a slurry and to retard the rate of set of the slurry. Martin, U.S. Pat. No. 3,234,154 teaches to employ glucoheptonic acid or a water-soluble salt thereof as a retarder in combination with sulfonated polystyrene or sulfonated polyvinyltoluene as a fluid loss additive and a lignin derivative as a stabilizer. Martin, U.S. Pat. No. 3,662,830, teaches a two component borate and alkali or alkaline earth metal salt of lignosulfonic acid retarder may be used in combination with cellulose derivatives, sulfonated polystyrene or sulfonated polyvinyltoluene. In a commonly assigned U.S. patent application by Crinkelmeyer et al., allowed Ser. No. 824,022 filed Aug. 12, 1977 (a continuation-in-part of Ser. No. 546,845 filed Feb. 3, 1975, now abandoned), a retarded low fluid loss cement slurry is taught containing a lignoamine or lignosulfonate, a borate, a polyamino compound, and a carbonate or bicarbonate.
Notwithstanding the foregoing, however, those skilled in the art (e.g., see Martin, U.S. Pat. No. 3,234,l54 at column 1, lines 45-52), recognize that an additive which performs well alone may not be compatible in the presence of other additives. Thus, as is shown in the comparison runs below, sodium glucoheptonate cannot be used to retard slurries such as those taught by Gibson et al., containing a polyamine compound as a fluid loss additive because the sodium glucoheptonate severely adversely affects the fluid loss properties of the slurry.
Another factor to be considered, especially in offshore cementing operations, is logistics. Since offshore platforms normally do not have equipment for dry blending dry additives with the neat cement, it is highly desirable to assure a uniform slurry that all components of a cement slurry except the neat cement be substantially water-soluble so that the additives may be readily and accurately metered into the mix water just prior to the on-the-fly addition of the neat cement. It is also highly desirable, especially for offshore work, to have a system which can utilize mild brines or sea water as the mix water.
Thus, one particular problem addressed by the present invention was that of providing a retarder adapted for offshore use which was compatible with a cement system such as that of Gibson et al., i.e., which contains a polyamino compound as a fluid loss additive; which was a liquid or liquifiable; and which resulted in a system that could employ fresh water or sea water as the mix water.
The teachings of each of the patents and the patent application hereinabove referred to are expressly incorporated herein.